It has been known for a long time to use containers of a collapsible type. The contents can be both in liquid and in powder form.
By a container of a collapsible type is meant the type of container that consists of thin flexible walls which are joined in connection portions to define a compartment. The volume of the compartment depends on the relative distance between the walls, which means that the volume depends on the filling ratio of the container. This type of containers may have a number of different handle types, for instance gas-filled handles for improved grippability.
Containers of a collapsible type are as a rule filled through a duct/opening which is defined by two opposite walls of the container. Such filling occurs with the container in an upright position, in which case the filling nozzle can act essentially in the vertical direction and be introduced into the duct between the two walls. This is a method that is well established and well functioning when supplying fluids in liquid form. The same method, however, causes great problems when supplying fluids in gaseous form due to difficulties in providing a gas-tight seal around the nozzle while the gas is being supplied. Additional problems arise when the gas-filled duct is to be sealed.
A solution to these problems is that the duct is filled with gas through a check valve integrated in the container. This technique is very expensive to apply to mass-produced containers, such as food containers where the duct is to be filled only once.
WO2005/030599 discloses a method and a device for gas filling and sealing of a duct intended to be filled with gas and positioned in a container of a collapsible type, where the duct has an inlet arranged in one of its side walls. During filling with gas, that part of the container which comprises the inlet is clamped between an abutment and a gas module which is axially movable towards the abutment in such a manner that one of the two side walls included in the duct is allowed to bulge to form a free passage into the duct, in response to a gas flow supplied from the gas module. After completion of the gas filling, the duct is sealed. However, it is difficult to ensure a correct filling ratio of the ducts, that is a repeatable and sufficiently high pressure, since it is difficult to seal against the inlet during filling. This can be compensated for by taking a pressure above atmospheric from the used source of compressed air based on the estimated pressure loss due to leakage. However, repeatability is insufficient, which results in some ducts being insufficiently filled whereas others are filled to such an extent that they quite simply burst.
Therefore there is a need for a method and a device for gas filling of such ducts in collapsible containers, independently of the purpose of the gas-filled ducts, in which the necessary repeatability is ensured.